Mac: Add default tooltip implementation (issue #770).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk@1119 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Mac: Fix compile error (issue #630).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk@1121 5089003a-bbd8-11dd-ad1f-f1f9622dbc98